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Defecation 1: Testing a hypothesis for pelvic striated muscle action to open the anorectum
1St Vincent's Hospital, University of New South Wales, Sydney, NSW, Australia. pp@kvinno.com
Techniques in Coloproctology
|August 15, 2012
Summary
Pelvic floor muscles actively open the anorectal lumen during defecation by stretching the rectum. This coordinated muscle action reduces resistance, aiding in the expulsion of feces.
Area of Science:
- Anorectal physiology
- Pelvic floor biomechanics
- Defecation dynamics
Background:
- Investigated the hypothesis of active pelvic muscle involvement in opening the anorectal lumen during defecation.
- Utilized observational study design to evaluate defecation mechanics.
Purpose of the Study:
- To assess the role of pelvic striated muscles in actively widening the anorectal lumen.
- To understand the biomechanical forces contributing to rectal lumen expansion during defecation.
Main Methods:
- Video imaging studies (defecography, MRI defecating proctograms) were performed on three groups of female patients.
- Included patients with idiopathic fecal incontinence, obstructive defecation, and healthy controls.
Main Results:
- The anorectum diameter doubled during defecation due to bidirectional stretching by muscle forces.
- Pelvic floor muscles contract and relax in stages: puborectalis relaxes, levator plate (LP) and conjoint longitudinal muscle contract, followed by pubococcygeus contraction and external anal sphincter relaxation.
- These actions open the anorectal angle and anterior rectal wall, facilitating fecal expulsion.
Conclusions:
- Pelvic striated muscles actively contribute to opening the rectal lumen during defecation.
- This muscular action reduces anorectal resistance to fecal expulsion.
- Further electromyographic studies are recommended to confirm these findings.
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